Various prostheses have been developed for replacing joints in human bodies, including joints for the toes and fingers. Many of these prostheses are formed of elastomeric polymeric material in one piece with a hinge section positioned in the joint area. Example of such prostheses are shown in U.S. Pat. Nos. 3,462,765 and 3,875,594 to Dr. A. B. Swanson. Another type of prosthesis is of the ball and socket type design, for example that shown in U.S. Pat. No. 4,304,011 issued to Whelan, III.
A further type of prosthesis is formed from two members, one of which is inserted into each of the respective bones in the joint. Alternatively only one side of the joint is replaced with a concavely surfaced implant that articulates against the convex rounded bony structure of the remaining bone in the joint (for example, a metatarsal head). The members of the prosthesis have enlarged heads that are adapted to engage each other or the bone to form a pivotable connection. Examples of such joints are shown in U.S. Pat. Nos. 4,242,759 to White, 4,642,122 to Steffee and 4,231,121 to Lewis, and 4,685,919 to Niwa, et al. The prosthesis of the present invention pertains to the latter type. A problem which has occurred with such implants is that in some cases motion between the concave surface of the implant and the convex surface of the bone becomes limited, such as by soft tissue fibrosis, with the result that motion is lost. The present invention overcomes this problem by providing a one-piece implant having dual articulating means which will assure that bending motion can always be achieved.
Briefly summarized, the present invention provides an improved prosthetic toe joint adapted for replacement of a human toe joint which includes at least one one-piece member for implantation into the bone of the joint. The implant of this invention has a concave articulating surface which articulates against another one-piece component having a mating convex surface or against a mating convex bone surface. This one part component is provided with a flexible hinge section at the junction of its stem and the enlarged head portions. The hinge section is formed from a section of the stem which extends laterally outwardly on both sides of the stem portion adjacent the junction with the head. The laterally enlarged section is provided with a longitudinal channel extending through its midsection to form a hinge. Each of the one-piece components is preferably molded of a flexible elastomeric, physiologically inert material, for example medical grade silicone elastomer of the type marketed by Dow Corning Corporation, Midland, Michigan. One or both of the articular surfaces of the one-piece components may be provided with wear-resistant caps for example a layer of titanium metal which is integral with the articular surface.
Other purposes and objects of the invention will be apparent to persons skilled in the art relating to prostheses of this general type and from a reading of the following specification and inspection of the drawings.